The Efficacy of Vectron 20？WP, Etofenprox, for Indoor Residual Spraying in Areas of High Vector Resistance to Pyrethroids and Organochlorines in Zambia
The selection of insecticide resistance in malaria vectors has the potential to compromise any insecticide-based vector control programme. To ensure that the insecticides used for indoor residual spraying and insecticide-treated nets in Zambia remain effective and their choice is evidence based, insecticide resistance surveillance and monitoring are essential. This study assessed and compared the residual efficacy of etofenprox (Vectron 20？WP), an ether pyrethroid, at 0.1？g/m2 with pyrethroids: bifenthrin (Bistar 10？WP) and lambda-cyhalothrin (Icon 10 CS) at 25？mg/m2 for indoor residual spraying. We also assessed the resistance status of etofenprox to local malaria vectors, An. funestus s.s and An. gambiae s.s, using World Health Organization standard protocols. The residual efficacy of Vectron 20？WP on cement, rendered walls of houses lasted for four months with 100% mortality. By the eighth month, the killing effect had reduced to 73.8% compared to 63.3% for bifenthrin and 77.0% for lambda-cyhalothrin. Susceptibility tests using standard World Health Organization assays on An. gambiae s.s showed susceptibility to etofenprox (0.1%) but some resistance was detected to Anopheles funestus s.s. The product is recommended as an ideal insecticide for indoor residual spraying for malaria control in Zambia as part of a resistance management programme in selected areas of the country. 1. Introduction Globally, about 515 million malaria cases with over one million deaths occur annually in tropical and subtropical regions [1]. The greatest toll is exacted in sub-Saharan Africa, particularly in children and pregnant women [2, 3]. This huge burden of disease is as a consequence of the excellent vectorial competence of the three major vectors of malaria: Anopheles gambiae s.s, Anopheles arabiensis, and Anopheles funestus [4, 5]. Malaria remains a major public health challenge and continues to severely undermine the socioeconomic growth in sub-Saharan Africa [6]. In the absence of a vaccine, much of the malaria control efforts rely primarily on effective treatment with antimalaria drugs and prevention through transmission-blocking vector control interventions [7, 8]. Nevertheless, effectiveness of malaria control is threatened by the increasing levels of both drug resistance in Plasmodium parasites [9] and insecticide resistance in Anopheles vectors [10]. The main thrust contemporary vector control interventions, that is, indoor residual spraying (IRS) and insecticide treated nets (ITNs), are insecticide based [11]. However, the arsenal of insecticides is so limited
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